What is the point, really, of kissing? Humans make such a big deal of it, but almost no other animals smooch.

A new study out of Oxford University suggests that kissing may actually have a purpose beyond the obvious — it’s a mating audition. Potential mates are doing a taste test. And that could explain why women and guys who think they’re good-looking enjoy it more than other people do.

Kissing, which is practiced in almost every human society in various forms, is something of a mystery to those who study mating behavior. Chimps and bonobos kiss, but not with the same intensity or high levels of mooniness before and after the act that Homo sapiens display. There are three working theories about why we, as opposed to other species, like to lock lips: kissing can arouse, it cements relationships together or it’s a trial run of a potential mate.

Two researchers from Oxford’s department of experimental psychology, Rafael Wlodarski and Robin Dunbar, provide evidence for the latter explanations in their latest investigation. They set up an online survey and asked about 900 adults (about two-thirds of whom were women) to answer questions about how important kissing was in both long and short relationships. Overall, women valued kissing more than men (no surprise), but guys who rated themselves as more attractive than others or who had lots of girlfriends also placed more emphasis on the smooch.

That makes sense, say the researchers, since both women and good-looking guys tend to be more picky about their mating partners. For women, bearing and raising children is a huge investment of their life and health, so they want to choose the right co-parent. As anthropologist Helen Fisher told U.S. News and World Report, “When you get a highly intelligent, pair-bonding species that requires years to raise a baby, you evolve more and more brain mechanisms to weed out the losers.” The hottie guys are picky because, well, they can be; they have a lot of choices, so they need a way to winnow them down. Kissing, says the Oxford team, may therefore be a way of trying on potential partners.

“Mate choice and courtship in humans is complex,” Dunbar said in a statement discussing the work. “It involves a series of periods of assessments where people ask themselves, ‘Shall I carry on deeper into this relationship?’” The early judgment calls are all based on facial, body and social cues. “Then assessments become more and more intimate as we go deeper into the courtship stages,” he said, “and this is where kissing comes in.”

How does a kiss determine mateworthiness? It’s not really clear, but some philematologists (those are the people who study kissing) believe that it has to do with smell. In her book The Science of Kissing, Sheril Kirshenbaum cites Claus Wedekind, who she says found that “women are most attracted to the scent of men who have a very different genetic code for their immune system in a region of DNA known as the major histocompatibility complex.” Having different DNA from the individual you are kissing heightens the chance of having healthy offspring should the kissing lead somewhere. And juxtaposing two orbicularis oris muscles in a state of contraction is usually more fun than having a genetic test.

Other scientists believe women send off a signal if they’re ovulating that can be subconsciously detected if a mate is close enough. As the authors of a study published in the Archives of Sexual Behaviorput it, “It is unclear, for example, whether kissing aids in the process of mate assessment by facilitating the evaluation of pheromonal cues for overall health, genetic fitness, or menstrual-cycle phase and fertility, or alternatively by aiding gustatory assessment of skin oils and saliva compounds.” (Translation: it could be a subconscious thing, or it could be that mates are actually figuring out whether each other smells good.)

Women in the study also ranked kissing as more important for longer relationships, suggesting it was a way of communicating and enhancing affection and attachment. In fact, more kissing was strongly correlated than more sex with a higher-quality relationship (although the people who had a lot of both had the highest relationship satisfaction). Moreover, the researchers suggest that although kissing does cause arousal, arousal doesn’t seem to be what is driving people to kiss.